[https-proxy-agent] Support dynamic headers (#174)

.changeset/tidy-jobs-refuse.md

@@ -0,0 +1,5 @@
+---
+'https-proxy-agent': minor
+---
+
+"headers" option can now be a function

packages/https-proxy-agent/src/index.ts

@@ -3,7 +3,7 @@ import * as tls from 'tls';
 import * as http from 'http';
 import assert from 'assert';
 import createDebug from 'debug';
-import { OutgoingHttpHeaders } from 'http';
+import type { OutgoingHttpHeaders } from 'http';
 import { Agent, AgentConnectOpts } from 'agent-base';
 import { parseProxyResponse } from './parse-proxy-response';
 
@@ -25,7 +25,7 @@ type ConnectOpts<T> = {
 
 export type HttpsProxyAgentOptions<T> = ConnectOpts<T> &
 	http.AgentOptions & {
-		headers?: OutgoingHttpHeaders;
+		headers?: OutgoingHttpHeaders | (() => OutgoingHttpHeaders);
 	};
 
 /**
@@ -44,7 +44,7 @@ export class HttpsProxyAgent<Uri extends string> extends Agent {
 	static protocols = ['http', 'https'] as const;
 
 	readonly proxy: URL;
-	proxyHeaders: OutgoingHttpHeaders;
+	proxyHeaders: OutgoingHttpHeaders | (() => OutgoingHttpHeaders);
 	connectOpts: net.TcpNetConnectOpts & tls.ConnectionOptions;
 
 	get secureProxy() {
@@ -101,7 +101,10 @@ export class HttpsProxyAgent<Uri extends string> extends Agent {
 			socket = net.connect(this.connectOpts);
 		}
 
-		const headers: OutgoingHttpHeaders = { ...this.proxyHeaders };
+		const headers: OutgoingHttpHeaders =
+			typeof this.proxyHeaders === 'function'
+				? this.proxyHeaders()
+				: { ...this.proxyHeaders };
 		const host = net.isIPv6(opts.host) ? `[${opts.host}]` : opts.host;
 		let payload = `CONNECT ${host}:${opts.port} HTTP/1.1\r\n`;
 

packages/https-proxy-agent/test/test.ts

@@ -188,7 +188,7 @@ describe('HttpsProxyAgent', () => {
 			assert.equal('ECONNREFUSED', err.code);
 		});
 
-		it('should allow custom proxy "headers"', async () => {
+		it('should allow custom proxy "headers" object', async () => {
 			const agent = new HttpsProxyAgent(serverUrl, {
 				headers: {
 					Foo: 'bar',
@@ -205,6 +205,29 @@ describe('HttpsProxyAgent', () => {
 			socket.destroy();
 		});
 
+		it('should allow custom proxy "headers" function', async () => {
+			let count = 1;
+			const agent = new HttpsProxyAgent(serverUrl, {
+				headers: () => ({ number: count++ }),
+			});
+
+			const connectPromise = once(server, 'connect');
+			http.get({ agent });
+
+			const [req, socket] = await connectPromise;
+			assert.equal('CONNECT', req.method);
+			assert.equal('1', req.headers.number);
+			socket.destroy();
+
+			const connectPromise2 = once(server, 'connect');
+			http.get({ agent });
+
+			const [req2, socket2] = await connectPromise2;
+			assert.equal('CONNECT', req2.method);
+			assert.equal('2', req2.headers.number);
+			socket2.destroy();
+		});
+
 		it('should work with `keepAlive: true`', async () => {
 			server.on('request', (req, res) => {
 				res.end(JSON.stringify(req.headers));